U.S. patent application number 15/024796 was filed with the patent office on 2016-08-04 for amine precursors for depositing graphene.
The applicant listed for this patent is BASF SE, MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN E.V.. Invention is credited to Yoshikazu Ito, Klaus Mullen, Hermann Sachdev, Matthias Georg Schwab.
Application Number | 20160225991 15/024796 |
Document ID | / |
Family ID | 49293531 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160225991 |
Kind Code |
A1 |
Schwab; Matthias Georg ; et
al. |
August 4, 2016 |
AMINE PRECURSORS FOR DEPOSITING GRAPHENE
Abstract
The present invention relates to the use of an amine precursor
of formula I (X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I) or its
ammonium salts for depositing a graphene film having a nitrogen
content of from 0 to 65% by weight on a substrate S1 by chemical
vapor deposition (CVD), wherein R.sup.1 is selected from (a)
C.sub.1 to C.sub.10 alkanediyl, which may all optionally be
interrupted by at least one of O, NH and NR.sup.2, (b) alkenediyl,
which may all optionally be interrupted by at least one of O, NH
and NR.sup.2, (c) alkynediyl, which may all optionally be
interrupted by at least one of O, NH and NR.sup.2, (d) C.sub.6 to
C.sub.20 aromatic divalent moiety, and (e) CO and CH.sub.2CO,
X.sup.1 is selected from H, OH, OR.sup.2, NH.sub.2, NHR.sup.2, or
NR.sup.2.sub.2, wherein two groups X.sup.1 may together form a
bivalent group X.sup.2 being selected from a chemical bond, O, NH,
or NR.sup.2, R.sup.2 is selected from C.sub.1 to C.sub.10 alkyl and
a C.sub.6 to C.sub.20 aromatic moiety which may optionally be
substituted by one or more substituents X.sup.1, n is 1, 2, or
3.
Inventors: |
Schwab; Matthias Georg;
(Mannheim, DE) ; Mullen; Klaus; (Koln, DE)
; Sachdev; Hermann; (Saarbrucken, DE) ; Ito;
Yoshikazu; (Sendai, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE
MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN
E.V. |
Ludwigshafen
Munchen |
|
DE
DE |
|
|
Family ID: |
49293531 |
Appl. No.: |
15/024796 |
Filed: |
September 29, 2014 |
PCT Filed: |
September 29, 2014 |
PCT NO: |
PCT/IB2014/064919 |
371 Date: |
March 24, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/0002 20130101;
H01L 51/42 20130101; H01L 51/0558 20130101; C23C 16/26 20130101;
C01B 32/186 20170801; H01L 51/003 20130101; H01L 51/50 20130101;
H01L 51/0045 20130101; H01L 51/002 20130101; C23C 16/30
20130101 |
International
Class: |
H01L 51/00 20060101
H01L051/00; C23C 16/30 20060101 C23C016/30 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2013 |
EP |
13187091.7 |
Claims
1. A method for depositing a graphene film using a precursor of
formula I (X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I) or its
ammonium salt, the graphene film having a nitrogen content of from
0 to 65% by weight on a substrate S1 by chemical vapor deposition
(CVD), wherein R.sup.1 is selected from (a) C.sub.1 to C.sub.10
alkanediyl, which may all be interrupted by at least one of O, NH
and NR.sup.2, (b) alkenediyl, which may all be interrupted by at
least one of O, NH and NR.sup.2, (c) alkynediyl, which may all be
interrupted by at least one of O, NH and NR.sup.2, (d) C.sub.6 to
C.sub.20 aromatic divalent moiety, and (e) CO, CH.sub.2CO, X.sup.1
is selected from the group consisting of H, OH, OR.sup.2, NH.sub.2,
NHR.sup.2, and NR.sup.2.sub.2, wherein two groups X.sup.1 may
together form a bivalent group X.sup.2 being selected from a
chemical bond, O, NH, or NR.sup.2, R.sup.2 is selected from the
group consisting of C.sub.1 to C.sub.10 alkyl and a C.sub.6 to
C.sub.20 aromatic moiety which may be substituted by one or more
substituents X.sup.1, n is 1, 2, or 3.
2. The method of claim 1, wherein R.sup.1 is selected from linear
or branched C.sub.1 to C.sub.10 alkyl, which may be interrupted by
O or NH, and a divalent C.sub.6 to C.sub.12 aromatic moiety.
3. The method of claim 1, wherein X.sup.1 is H and R.sup.1 is
selected from linear or branched C.sub.1 to C.sub.5 alkanediyl and
a divalent C.sub.6 to C.sub.12 aromatic moiety
4. The method of claim 1, wherein X.sup.1 is selected from OH or
OR.sup.2 with R.sup.2 being selected from linear or branched
C.sub.1 to C.sub.5 alkyl.
5. The method of claim 1, wherein X.sup.1 is selected from
NH.sub.2, NHR.sup.2 or NR.sup.2.sub.2 with R.sup.2 being selected
from linear or branched C.sub.1 to C.sub.5 alkyl.
6. The method of claim 1, wherein the amine precursor is selected
from the group consisting of methylamine, ethylamine, ethanol
amine, methyldiamine, ethylenediamine, aniline, and combinations
thereof.
7. The method of claim 1, wherein the amine precursor is selected
from the group consisting of formamide, acetamide, and combinations
thereof.
8. The method of claim 1, wherein the substrate S1 is selected from
the group consisting of an insulating substrate, a semiconducting
substrate, a metal substrate, a conducting substrate, and
combinations thereof.
9. A process for depositing a graphene film having a nitrogen
content of from 0 to 65% by weight on a substrate S1, the process
comprising: (a) providing an amine precursor of formula I
(X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I) or its ammonium salt for
depositing a graphene film having a nitrogen content of from 0 to
65% by weight on a substrate S1 by chemical vapor deposition (CVD),
wherein R.sup.1 is selected from (a) C.sub.1 to C.sub.10
alkanediyl, which may all be interrupted by at least one of O, NH
and NR.sup.2, (b) alkenediyl, which may all be interrupted by at
least one of O, NH and NR.sup.2, (c) alkynediyl, which may all be
interrupted by at least one of O, NH and NR.sup.2, (d) C.sub.6 to
C.sub.20 aromatic divalent moiety, and (e) CO, CH.sub.2CO, X.sup.1
is selected from the group consisting of H, OH, OR.sup.2, NH.sub.2,
NHR.sup.2, and NR.sup.2.sub.2, wherein two groups X.sup.1 may
together form a bivalent group X.sup.2 being selected from a
chemical bond, O, NH, or NR.sup.2, R.sup.2 is selected from the
group consisting of C.sub.1 to C.sub.10 alkyl and a C.sub.6 to
C.sub.20 aromatic moiety which may optionally be substituted by one
or more substituents X.sup.1, n is 1, 2, or 3. (b) providing the
substrate S1, (c) activating the amine precursor in order to
decompose the amine precursor, and (d) depositing the graphene film
on the substrate S1.
10. The process according to claim 9, wherein the amine precursor
is selected from a C.sub.1 to C.sub.4 alkylamine and steps (c) and
(d) are performed in the presence of H.sub.2 in order to deposit a
graphene film being essentially free from nitrogen.
11. The process according to claim 9, wherein the amine precursor
is selected from a C.sub.1 to C.sub.4 alkylamine and steps (c) and
(d) are performed under inert conditions in order to deposit a
graphene film having a nitrogen content of from 10.sup.-20 atom %
to 65% by weight.
12. The process according to claim 9, wherein the amine precursor
is selected from a C.sub.1 to C.sub.4 alkanolamine and steps (c)
and (d) are performed in the presence of H.sub.2 in order to
deposit a graphene film having a nitrogen content of from
10.sup.-20 atom % to 65% by weight.
13. The process according to claim 9, wherein the amine precursor
is selected from a C.sub.1 to C.sub.4 alkanolamine or methylamine
and steps (c) and (d) are performed under inert conditions in order
to deposit a graphene film being essentially free from
nitrogen.
14. The process according to claim 9, further comprising a step (e)
of transferring the graphene film from the substrate S1 to a
substrate S2, which is different from the substrate S1.
15. A layered assembly comprising a graphene film on a substrate S1
or S2, said layered assembly being obtainable by the process
according to claim 9, and said graphene film having a nitrogen
content of from 0 to 65% by weight.
16. The process according to claim 9 further comprising a step
between step (b) and step (c) for at least partially transferring
the amine precursor into a gas phase.
17. The process according to claim 16 wherein the amine precursor
is in a liquid state prior to at least partially transferring the
amine precursor into a gas phase.
18. The process according to claim 16 wherein the amine precursor
is in a solid stated prior to at least partially transferring the
amine precursor into a gas phase.
Description
[0001] The invention relates to the use of amine precursors for
depositing graphene and a process of depositing graphene using such
amine precursors via chemical vapor deposition (CVD).
BACKGROUND OF THE INVENTION
[0002] Graphene ideally consists of sp.sup.2-hybridized carbon
atoms arranged in a two-dimensional layer and hexagonal array and
is the constituting building block of macroscale graphite, with
long-range .pi.-conjugation, which results in extraordinary
thermal, mechanical, and electronic properties. For manipulating
the physical and chemical properties of graphene materials,
chemical functionalization is of great interest.
[0003] In reality graphene can exhibit intrinsic structural
defects, e.g. 5,7,8 membered ring structures, as well as
heteroatoms such as boron, nitrogen, oxygen and others, which
influence its quality. Doping of graphene means that carbon atoms
of the regular graphene lattice can be replaced by those
heteroatoms, which may be uncharged or charged or saturated with
other functional groups.
[0004] In principle, graphene materials can be chemically
functionalized. According to a first approach, the aromatic basal
plane is modified by addition reaction with C.dbd.C bonds. At
present, this is the commonly favored approach. Alternatively,
chemical functionalization can be effected at the edge of the
graphene material, thereby resulting in edge-functionalized
graphene (e.g. substituting the edge-bonded residues by another
chemical group). This approach is of particular relevance for those
graphene materials which have confined dimensions either in just
one direction of the plane (graphene nanoribbons) or in both
directions of the plane (graphene molecules, i.e. very large
polycyclic aromatic compounds).
[0005] Graphene exhibits a semi-metal characteristic. The
semi-metal characteristic is due to a conduction band and a valance
band overlapping each other at only one point (Dirac point).
Furthermore, graphene has two-dimensional ballistic transport
characteristic. Thus, a mobility of electrons in graphene is
generally very high. Because graphene is a zero-gap semiconductor,
a field-effect transistor, in which graphene is used as a channel
exhibits a very large off-current and a very small on-off ratio.
Thus, it is difficult to apply graphene to a field effect
transistor. To form a band gap in graphene, it is necessary to
break the sublattice symmetry of graphene. In this regard, boron
(B) or nitrogen (N) doped graphene, a two dimensional material, is
discussed as a promising system with tunable electronic properties.
Theory as well as experimental studies indicate that B- or N-doped
graphene reveals p- or n-type semiconductor characteristics
accompanied by a band gap opening and therefore, graphene with
controllable electronic properties is expected to be a promising
material for the low cost and eco-friendly replacement of current
electronic devices. Furthermore, transparent and doped graphene
films are considered for new applications in organic electronic
devices such as OLED's and organic solar cells and
photodetectors.
[0006] So far, few methods for generating N-doped graphene are
described, such as thermal or plasma treatments of graphitic
materials e.g. by thermal CVD of methane and ammonia gas (Wei, D.;
Liu, Y.; Wang, Y.; Zhang, H.; Huang, L.; Yu, G. Nano Lett. 2009, 9,
1752) or molecular precursors like pyridine (Jin, Z.; Yao, J.;
Kittrell, C.; Tour, J. M. ACS Nano 2011, 5, 4112) or acetonitrile
(Reddy, A. L. M.; Srivastava, A.; Gowda, S. R.; Gullapalli, H.;
Dubey, M.; Ajayan, P. M. ACS Nano 2010, 4, 6337-6342) or
1,3,5-triazine (Lu, Y.-F.; Lo, S.-T.; Lin, J.-C.; Zhang, W.; Lu,
J.-Y., Liu, F.-H. ACS Nano 2013, 7, 6522-6532) on a Cu substrate or
by exposing graphene to a nitrogen (Wang, Y.; Shao, Y.; Matson, D.
W.; Li, J.; Lin, Y. ACS Nano 2010, 4, 1790-1798) or ammonia (Lin,
Y. C.; Lin, C. Y.; Chiu, P. W. Appl. Phys. Lett. 2010, 96, 133110)
containing plasma discharge.
[0007] L. Qu, Y. Liu, J.-B. Baek, L. Dai, ACS Nano 2010, 4, 1321
describe the growth of nitrogen doped graphene on sputter-coated Ni
substrates by chemical vapor deposition from reactive gas mixtures
containing ammonia.
[0008] US 20110313194 A1 discloses a graphene comprising a
structure of carbon (C) atoms partially substituted with boron (B)
atoms and nitrogen (N) atoms, where the graphene has a band gap.
Preparation of the graphene comprises performing a chemical vapor
deposition (CVD) method using N.sub.2 or NH.sub.3 as an N
precursor, BCl.sub.3 as a B precursor and borazine or ammonia
borane as a B--N precursor. C.sub.2H.sub.4 and CH.sub.4 are
explicitly mentioned as C precursors.
[0009] CN 102605339 A discloses process for preparing
nitrogen-doped graphene comprising placing a metal catalyst in a
reactor, heating the catalyst at 200-600 degrees C. under
non-oxidizing atmosphere, inletting carbon and nitrogen source in
the reactor to react, and processing chemical vapor deposition to
obtain the nitrogen-doped graphene. The nitrogen source comprises
pyridine, pyrrole, pyrazine, pyridazine, pyrimidine, cytosine,
uracil, thymine or purine, and the carbon source comprises
methanol, ethanol, benzene, methylbenzene and chlorobenzene.
[0010] CN 102887498 A discloses a preparation process of
nitrogen-doped graphene by chemical vapor deposition, followed by a
doping process. The method includes providing a substrate (Cu, Fe
and/or Ni foil) and solid and/or liquid organic carbon source
compound (ferrocene, cobaltocene, nickelocene and/or
bis-(cyclopentadienyl)manganese), prepaging 5-30% by weight
solution or suspension of the organic carbon source, coating the
carbon source solution or suspension to the surface of the
substrate, heating the coated substrate to 500-1300.degree. C.
under oxygen-free or vacuum condition. After the deposition of the
graphene film a gaseous N source compound (N.sub.2, NH.sub.3 and/or
methyl amine) is aerated by a flow of 10-200 cm.sup.3/s and a C/N
molar ratio of 2-20:1 for reaction to give N-doped graphene, and
purifying the obtained N-doped graphene by soaking in dil. acid
soln. for 0.1-24 h.
[0011] It is an object of the present invention to provide a cost
efficient and simple process for depositing graphene materials
which may optionally be N-doped. It is a further object of the
present invention to provide a process for depositing optionally
N-doped Graphene. It is yet another object of the present invention
to enable a more facile graphene formation by gas phase activation.
It is yet another object of the present invention to enable direct
graphene formation without the use of additional hydrogen. It is
yet another object of the invention to provide a process for
directly depositing doped graphene without any additional doping
step. It is yet another object of the present invention to prepare
a graphene having a better sheet resistance.
SUMMARY OF THE INVENTION
[0012] One aspect of the present invention is the use of an amine
precursor of formula I
(X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I)
[0013] or its ammonium salts for depositing a graphene film having
a nitrogen content of from 0 to 65% by weight on a substrate S1 by
chemical vapor deposition (CVD),
[0014] wherein [0015] R.sup.1 is selected from [0016] (a) C.sub.1
to C.sub.10 alkanediyl, which may all optionally be interrupted by
at least one of O, NH and NR.sup.2, [0017] (b) alkenediyl, which
may all optionally be interrupted by at least one of O, NH and
NR.sup.2, [0018] (c) alkynediyl, which may all optionally be
interrupted by at least one of O, NH and NR.sup.2, [0019] (d)
C.sub.6 to C.sub.20 aromatic divalent moiety, and [0020] (e) CO and
CH.sub.2CO, [0021] X.sup.1 is selected from H, OH, OR.sup.2,
NH.sub.2, NHR.sup.2, or NR.sup.2.sub.2, wherein two groups X.sup.1
may together form a bivalent group X.sup.2 being selected from a
chemical bond, O, NH, or NR.sup.2, [0022] R.sup.2 is selected from
C.sub.1 to C.sub.10 alkyl and a C.sub.6 to C.sub.20 aromatic moiety
which may optionally be substituted by one or more substituents
X.sup.1, [0023] n is 1, 2, or 3.
[0024] A further aspect of the present invention is a process for
depositing graphene having a nitrogen contend of from 0 to 65% by
weight on a substrate S1, the process comprising [0025] (a)
providing an amine precursor of formula I or its ammonium salt as
described herein, [0026] (b) providing the substrate S1, [0027] (c)
if the amine precursor is in the solid or liquid state, at least
partly transferring the amine precursor into the gas phase, [0028]
(d) activating the amine precursor in order to decompose the amine
precursor, and [0029] (e) depositing the graphene film on the
substrate S1.
[0030] By using the amine precursors according to the present
invention the gas phase activation needed for the graphene
formation can be significantly lowered.
[0031] Furthermore the amine precursors enable a better and more
facile graphene formation, e.g. in the case of methylamine,
separation into methyl and amine radicals. Without to be bound to
any theory, inventors believe that the amine precursors generate
carbon growth species and radical species, which both lead to a
modified growth kinetic.
[0032] The process according to the present invention enables a
direct graphene formation without additional hydrogen, furthermore
it also allows the direct manufacture of N-containing or N-doped
graphene without the need of any further doping step, and in
addition also enables a co-doping with nitrogen and oxygen. The
graphene deposited by using the amine precursors according to the
present invention show a better sheet resistance.
DETAILS OF THE INVENTION
[0033] The amine precursors according to formula I
(X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I)
[0034] as described herein are useful for depositing a graphene
film having a nitrogen content of from 0 to 65% by weight on a
substrate S1 by chemical vapor deposition (CVD). Alternatively its
ammonium salts [(X.sup.1--R.sup.1).sub.n--NH.sub.(4-n)].sup.+ 1/m
Y.sup.m-, with Y being an inorganic or organic, preferably an
inorganic counter ion, and m being an integer from 1 to 3, may be
used.
[0035] R.sup.1 is selected from C.sub.1 to C.sub.10 alkanediyl,
alkenediyl, and alkynediyl, which may all optionally be interrupted
by at least one of O, NH and NR.sup.2, a C.sub.6 to C.sub.20
aromatic divalent moiety and CO or CH.sub.2CO; X.sup.1 is selected
from H, OH, OR.sup.2, NH.sub.2, NHR.sup.2, or NR.sup.2.sub.2;
R.sup.2 is selected from H, C.sub.1 to C.sub.10 alkyl and a C.sub.6
to C.sub.20 aromatic moiety which may optionally be substituted by
one or more substituents X.sup.1, wherein two groups X.sup.1 may
together form a bivalent group X.sup.2 being selected from a
chemical bond, O, NH, or NR.sup.2; and n is 1, 2 or 3.
[0036] As used herein, "aromatic moiety" means (i) aryl, such as
but not limited to phenyl or naphthyl, (ii) arylalkyl, such as but
not limited to toluyl or xylyl, or (iii) alkylaryl, such as but not
limited to benzyl. In a preferred embodiment aromatic moieties are
selected from phenyl, benzyl and naphthyl.
[0037] As used herein "alkyl", "alkenyl" and "alkynyl" means any
monovalent straight chain or cyclic, linear or branched radical
derived from the respective alkane, alkene or alkyne, respectively,
which may optionally be interrupted by O or NH.
[0038] The amine precursors may be primary amines (n=1), secondary
amines (n=2) or tertiary amines (n=3). Preferred are primary
amines. Ammonium salts of the amine precursors may also be
used.
[0039] Preferably R.sup.1 is selected from C.sub.1 to C.sub.10
alkanediyl, which may optionally be interrupted by O or NH. More
preferably R.sup.1 is selected from a linear or branched C.sub.2 to
C.sub.5 alkanediyl, which may optionally be interrupted by O atoms,
more preferably from C.sub.2 to C.sub.3 alkanediyl, most preferably
ethanediyl.
[0040] In a particular embodiment the precursors are unsubstituted
amines. Preferably X.sup.1 is H and R.sup.1 is selected from linear
or branched C.sub.1 to C.sub.5 alkanediyl and a divalent C.sub.6 to
C.sub.12 aromatic moiety, which means that X.sup.1--R.sup.1 is
selected from linear or branched C.sub.1 to C.sub.5 alkyl and a
monovalent C.sub.6 to C.sub.12 aromatic moiety.
[0041] In another embodiment X.sup.1 is selected from NH.sub.2,
NHR.sup.2 or NR.sup.2.sub.2 with R.sup.2 being selected from linear
or branched C.sub.1 to C.sub.5 alkyl.
[0042] In another embodiment the amine precursor is selected from
cyclic amines, such as but not limited to piperidine, piperazine,
and morpholine.
[0043] In another embodiment the amine precursor is formamide or
acetamide.
[0044] In yet another embodiment the precursors are alkanolamines
or ether derivatives thereof. Preferably X.sup.1 is selected from
OH or OR.sup.2 with R.sup.2 being selected from linear or branched
C.sub.1 to C.sub.5 alkyl, more preferably from C.sub.2 to C.sub.3
alkyl, most preferably ethyl.
[0045] Most preferably the amine precursor is selected from
methylamine, ethylamine, ethanol amine, methyldiamine,
ethylenediamine, aniline, and combinations thereof. Such amine
precursors may also be used in admixture with ammonia.
[0046] The graphene film may be deposited on the substrate S1 by
using the following process steps: [0047] (a) providing an amine
precursor of formula I or its ammonium salt as describe herein,
[0048] (b) providing the substrate S1, [0049] (c) if the amine
precursor is in the solid or liquid state, at least partly
transferring the amine precursor into the gas phase, [0050] (d)
activating the amine precursor in order to decompose the amine
precursor, and [0051] (e) depositing the graphene film on the
substrate S1.
[0052] After step (e) a further step (f) may be performed in order
to transfer the graphene film to a further substrate S2 as
described below.
[0053] The activation may be before the deposition on the substrate
S1, after the deposition of the amine precursor on the substrate S1
or partly before or after the deposition of the amine precursor on
the substrate S1.
[0054] The precursor may be used pure, diluted with an inert liquid
(NH.sub.3 liquid) or inert gas (He, Ar, N.sub.2) or together with
reactive gases (such as H.sub.2, CO, CO.sub.2) or higher
Hydrocarbons (C.sub.2H.sub.6, C.sub.2H.sub.4, C.sub.2H.sub.2, etc.)
or combined with other dopants such as B.sub.2H.sub.6, BF.sub.3,
BCl.sub.3, BBr.sub.3.
[0055] It must be emphasized that the amine precursors may be used
alone or in combination with other known precursors. It is
preferred to use only the amine precursors according to the present
invention
[0056] The amine precursors according to step (a) are generally
available on large scale on the market or may be produced by using
standard operations.
[0057] Any substrate S1 which is suitable for the growth of
graphene and compatible with the deposited graphene can be used in
step (b). Preferably, the substrate S1 should also be a material
which is compatible with the intended final use. However, as will
be discussed below in further detail with regard to a preferred
embodiment, it is also possible to provide the graphene film on a
substrate S1 first, and transferring the graphene film subsequently
to a different substrate S2, which may then become part of the
final device.
[0058] The substrate S1 of step (b) may generally be selected from
an insulating, semiconducting, or conducting substrate or a
combination thereof, depending on the application the graphene is
used.
[0059] The substrate can be chosen from a broad variety of
different materials. The substrate can be rigid but may also be
flexible (e.g. in the form of a foil). Appropriate substrates
include e. g. metals (such as copper, nickel, titanium, platinum
and alloys thereof), semiconductors (such as silicon, in particular
silicon wafers), inorganic substrates (such as oxides, e.g.
SiO.sub.2, glass, HOPG, mica, or any combination thereof), flexible
substrates that may be made of e.g. polymers such as polyethylene
terephthalate, polyethylene naphthalate, polymethyl methacrylate,
polypropylene adipate, polyimide or combinations or blends
thereof.
[0060] The substrate can be subjected to a pretreatment (such as
wet chemical etching, thermal annealing, annealing in a reactive
gas atmosphere, plasma cleaning treatment) so as to improve growth
of the graphene film and adhesion of the graphene film to the
substrate surface.
[0061] Step (c) is necessary to perform if the amine precursor is
not in the gaseous state of aggregation. In this case the amine
precursor needs to be transferred into the gaseous state.
[0062] This may be done, without limitation, by either direct
heating or use of an inert carrier gas and the precursors vapor
pressure or by a liquid flow or spray dosage or evaporation system,
and also by the use of an inert carrier gas.
[0063] In step (d) and (e) the amine precursor is activated and a
graphene film is deposited on the substrate by decomposition of the
amine precursor.
[0064] As used herein "activating" means any conversion of
precursors into active species capable of forming graphene, such as
but not limited to thermal activation, activation in a plasma or
activation by actinic radiation, or combinations thereof. Such
activation processes are generally known to a skilled person.
[0065] Preferably the activation comprises [0066] (a) thermal
activation in the gas phase or on the substrate, or a combination
thereof, [0067] (b) plasmachemical gas phase activation, [0068] (c)
plasmachemical gas phase activation in combination with a thermal
activation on the substrate, [0069] (d) hot filament CVD, [0070]
(e) direct laser activation of the precursor(s) by IR, VIS or UV
radiation, [0071] (f) UV, VIS and/or IR irradiation of the
substrate, the gas phase or both.
[0072] The graphene formation can take place either in the gas
phase without a substrate (e.g. by plasma CVD), in the gas phase
and being then deposited on a substrate, or directly on a
substrate.
[0073] In step (d) and (e) the surface temperature of the substrate
may vary from 4 K to 3000 K depending on the activation method. The
substrate may be cooled, heated directly or indirectly by any means
of energy transfer, such as thermal, laser, high frequency
irradiation, etc.
[0074] The gas phase temperature may be equal, higher or lower to
the substrate temperature, either be self-defined by the process
parameters or separately adjusted.
[0075] With or without the use of a substrate, the gas phase may be
thermally (250.degree. C.-2600.degree. C.) or plasma-chemically
activated with energy densities ranging from 0.001 W/cm.sup.3 to
1000 W/cm.sup.3
[0076] The precursor may be actively evaporated, and evaporated and
transported with an inert carrier gas or directly introduced
depending on its vapor pressure, boiling point of the precursor,
the decomposition temperature, the method of decomposition, and the
pressure used.
[0077] If thermal decomposition is used, it is preferred to use CVD
temperatures of from 500.degree. C. to 1400.degree. C., most
preferably of from 600.degree. C. to 1300.degree. C. In case of
decomposition by plasma activation, energy densities ranging from
0.001 W/cm.sup.3 to 1000 W/cm.sup.3 may generally be used.
[0078] In case of decomposition by actinic radiation a substrate
temperatures from 800.degree. C. to 1400.degree. C., most
preferably of from 900.degree. C. to 1200.degree. C. may be used.
The actinic radiation may be any radiation capable of breaking
chemical bonds, such as but not limited to UV, VIS or IR radiation
or a combination thereof.
[0079] In step (d) and (e) the total CVD pressure (irrespective of
the gas phase composition in which the active precursor(s) may be
present from 0.001% to 100%) may vary from 10.sup.-9 to 500000 hPa
depending on the boiling point of the precursor and the temperature
used. In one embodiment the pressure is from about 10.sup.-3 hPa to
about 1000 hPa, in particular from about 10-2 hPa to about 500 hPa.
In another embodiment the pressure is from about 10.sup.-9 hPa to
about 10.sup.-3 hPa, in particular from about 10.sup.-9 hPa to
about 10.sup.-4 hPa. In yet another embodiment the pressure is from
about 1100 hPa to about 200 000 hPa, in particular from about 1500
hPa to about 50 000 hPa. In yet another embodiment, atmospheric
pressure is used.
[0080] One particular advantage of the amine precursors according
to the present invention is the possibility to use atmospheric
pressure or above. In this way it is much easier to eliminate
negative effects by traces of atmospheric oxygen and nitrogen being
incorporated in the graphene.
[0081] In step (e) a graphene film is deposited on the substrate
S1. The graphene may be deposited on the substrate S1 directly or
indirectly. In case of indirect deposition the growth may take
place in the gas phase leading to any kind of single to multilayer
graphene, which is subsequently collected on the substrate S1.
Preferred is a direct deposition on the substrate S1.
[0082] Generally ideal graphene is an indefinitely large monolayer
of carbon atoms arranged in a two-dimensional honeycomb network.
"Graphene film" in the terms of the present invention is however
not restricted to a material consisting exclusively of single-layer
graphene (i.e. graphene in the proper sense and according to the
IUPAC definition), but, like in many publications and as used by
most commercial providers, rather denotes a material, which is
generally a mixture of a single-layer material, a bi-layer material
and a material containing 3 to 10 layers and sometimes even up to
100 layers. The individual lateral domains in the plane of the
graphene may range from a few nanometers to some mm each. The
precise ratio of the different materials (single, bi and multiple
layers) depends on the production process. In case of the present
invention, the material preferably contains about 0.01 to 99.99% by
covered substrate area of single-layer material, the remaining
portion being essentially material with other layer composition as
specified above.
[0083] The graphene film on the substrate consists of individual
intergrown domains, which can be single, double or multi layers.
The dimension of such domains can be nanoscale up to several mm. In
case no substrate is used, the dimension of the individual domains
is similar, but the aggregation can be globular or random.
[0084] In the terms of the present invention, "doped" relates to
hetero (non-carbon) atoms which are incorporated into the graphene
lattice, preferably by forming (chemical) bonds between nitrogen
and the carbon atoms of the graphene lattice. The nitrogen atoms
may be present at the edges as well as at the basal plane of the
graphene sheet. However, it is also possible that individual
nitrogen atoms are not part of the graphene lattice. Preferably,
all or nearly all of the nitrogen atoms provided via the respective
starting materials (see below) are incorporated into the graphene
lattice in the course of the synthesis reaction. However, it is
also possible that smaller amounts of nitrogen atoms be only
chemically or physically adsorbed on the surface of the graphene,
generally in form of the respective starting material used or of an
intermediate formed during the synthesis reaction. Usually, the
amount of said chemically or physically adsorbed nitrogen is less
than 10% of the amount of nitrogen forming covalent bonds with the
carbon atoms of the graphene lattice.
[0085] According to XPS (X-ray photoelectron spectroscopy), the
nitrogen-doped graphene according to the invention contains at
least part of the nitrogen in form of pyrrolic, pyridinic and/or
graphitic nitrogen atoms. Pyridinic nitrogen atoms are part of
six-membered rings and are bound to two carbon atoms, thus being
part of pyridine-like rings.
[0086] Also, hydrogen-containing or charged functions may be
present, such as but not limited to --NH.sub.3.sup.+, --NH.sub.2,
--NH.sub.2.sup.+, NH, NH.sup.+, etc. Appropriate counter-ions, such
as but not limited to OH.sup.-, Cl.sup.-, SO.sub.4.sup.2-,
PO.sub.4.sup.3-, or their partially protonated derivatives need to
be present.
[0087] During synthesis, they may also be oxidized fully or in
part, resulting in pyridinic N.sup.+--O.sup.- groups. Graphitic
nitrogen atoms are part of six-membered rings and are bound to
three carbon atoms, thus being bridging atoms between three fused
rings. Such graphitic nitrogen atoms are generally quaternized,
suitable counter-ions being single or multiple charged anions or
mixtures thereof, for example hydroxide and halides, phosphates,
sulfates, carbonates, in particular chloride. While graphitic
carbon atoms can be part of a large fused system, pyridinic
nitrogen atoms are either on the margin of the system or form
"defects" in the honeycomb network.
[0088] Without wishing to be bound by theory, it is assumed that
the nitrogen-doped graphene according to the invention may comprise
the following structural elements (the below structure is to be
understood only as a schematic and non-limiting illustration):
##STR00001##
[0089] Besides nitrogen (N) further hetero atoms, such as but not
limited to oxygen, boron and phosphorus or a combination thereof,
may be present in the graphene film. Particularly the co-doping of
graphene with nitrogen and boron and/or oxygen is of interest.
[0090] The co-doping of nitrogen with oxygen may also enable a
chemical functionalization. The co-doping with oxygen may be
achieved by either applying a specific N containing precursor and a
specified leak, a C--N--O containing precursor, or a C, an N and an
O precursor separately.
[0091] The deposited graphene film may be free from nitrogen or may
contain nitrogen in an amount of from 10.sup.-20 to 65% by weight.
The term "essentially free from nitrogen" as used herein means that
not nitrogen can be detected by using XPS, which is a standard
proof to validate the presence of nitrogen. This corresponds to a
nitrogen content below 0.3 atom %. Preferably the nitrogen content
is below 10.sup.-2 atom %, more preferably below 10.sup.-4 atom %,
even more preferably below 10.sup.-10 atom %, most preferably below
10.sup.-20 atom %. If nitrogen is present, the preferred amounts
are from the lower limit mentioned before to 20 atom %. In one
embodiment amounts of nitrogen in the graphene film up to 0.3 atom
% are used. In another embodiment amounts of nitrogen of from 0.3
to 15 atom % are used.
[0092] It was found that the nitrogen incorporation into the
graphene may be altered by using/not using hydrogen during the CVD
process in step (c). The type of nitrogen species may be altered
and favored towards the incorporation of nitrogen species with XPS
signals in the range of energies lower than 400 eV.
[0093] In one particular embodiment the amine precursor is selected
from a C.sub.1 to C.sub.4 alkylamine and step (c) is performed in
the presence of H.sub.2 in order to deposit a graphene being
essentially free from nitrogen.
[0094] In another particular embodiment the amine precursor is
selected from a C.sub.1 to C.sub.4 alkylamine and step (c) is
performed under inert conditions in order to deposit a graphene
having a nitrogen content of from 10.sup.-20 to 65% by weight.
[0095] "Inert conditions" means to use inert gases and conditions
which do not constitute to the film. An inert gas may be, but is
not limited to, a member of the noble gas family such as e. g.
argon.
[0096] In yet another particular embodiment the amine precursor is
selected from a C.sub.1 to C.sub.4 alkanolamine and step (c) is
performed in the presence of H.sub.2 in order to deposit a graphene
having a nitrogen content of from 10.sup.-20 to 65% by weight.
[0097] In yet another particular embodiment the amine precursor is
selected from a C.sub.1 to C.sub.4 alkanolamine or methylamine and
step (c) is performed under inert conditions in order to deposit a
graphene being essentially free from nitrogen.
[0098] It was surprisingly found that it is possible to obtain a
graphene, which is virtually nitrogen-free and from methylamine as
amine precursor.
[0099] The CVD of methylamine, ethylamine, ethanol amine, and
aniline reveal significant differences compared to the
corresponding precursors originating from unsubstituted aliphatic
(methane) or aromatic systems (benzene).
[0100] The formation of carbon films without significant
contribution of high quality graphene is usually indicated by broad
D and G modes without any resolved and narrow 2D modes of
appropriate line width in the Raman spectra indicating the
disordered nature of the films. This was observed for the direct
CVD of methane without hydrogen, but also in the case of aromatic
precursors like benzene and aniline. This finding might appear
surprising since the latter precursors possess six membered-ring
structures which formally resemble the graphene lattice. The
formation of carbon films from these compounds is assumed to take
place via either defragmentation to a manifold of individual gas
phase species leading to an uncontrolled nucleation and growth of
carbon films, although C--C bond formation between aromatic ring
systems may also occur. Graphene films were only formed in the
presence of additional hydrogen during the CVD of methane and
benzene, whereas e. g. methylamine does give rise to the presence
of high quality graphene in the deposits irrespective of the
presence of additional hydrogen.
[0101] By using the amine precursors according to the present
invention a graphene film having a thickness of from 1 to about 100
layers may be deposited. Preferably, the graphene film has a
maximum thickness t.sub.max of less than 1000 nm, more preferably
of less than 100 nm, even more preferably less than 30 nm or even
less than 10 nm; and a conductivity .sigma. of at least 100 S/cm,
more preferably at least 200 S/cm, even more preferably at least
250 S/cm.
[0102] Electrical conductivity is measured by a common four-probe
system with a Keithley 2700 Multimeter.
[0103] The graphene film can be continuous over an area of at least
1.times.10.sup.9 .mu.m.sup.2, more preferably at least
3.times.10.sup.8 .mu.m.sup.2, as determined by optical microscopy
at a magnification of 10.
[0104] With the term "continuous", it is meant that the substrate
surface is completely covered by the graphene film over the area
indicated and no substrate surface is detectable within this area
by optical microscopy.
[0105] As already mentioned above, the process of the present
invention also offers the opportunity to prepare the graphene film
on the substrate S1 first, and then transfer the graphene film to
another substrate S2. Just as an example, the substrate S1 may be
made of a material which is more convenient for preparing the
graphene film (e.g. high thermal stability, compatible with plasma
treatment at high temperature, etc.), whereas the substrate S2 is
adapted to the intended use of the final device.
[0106] Accordingly, in a preferred embodiment, the process of the
present invention comprises a further step (f), wherein the
graphene film is transferred to a substrate S2, which is different
from the substrate S1.
[0107] In principle, any of those materials mentioned above with
regard to the substrate S1 can be used for the substrate S2 as
well. Of course, a transfer of the graphene film from substrate S1
to substrate S2 is in particular of interest if S2 is different
from S1.
[0108] For some end applications, it might be of interest to
provide the graphene film on a flexible and/or transparent
substrate such as flexible and transparent polymer substrates. High
flexibility can be achieved by using a very thin substrate which
may have a thickness of about 10 to 1000 .mu.m. Furthermore, by
selecting appropriate materials such as polymers, a transparent
substrate can be provided. A transparent substrate is preferably
having a transmittance of at least 50%, more preferably at least
70%, even more at least 90% with regard to a wave length of from
200 to 2000 nm, more preferably 300 to 1000 nm, or 400 to 700
nm.
[0109] Thus, in a preferred embodiment, the substrate S2 is a
flexible and/or transparent substrate, such as a flexible and/or
transparent polymer foil (e.g. a foil made of polyethylene
terephthalate, polyethylene naphthalate, polymethyl methacrylate,
polypropylene adipate, polyimide or combinations or blends
thereof.
[0110] The graphene film on the substrate S1 has a lower surface
which is in contact with the substrate S1 and an uncovered upper
surface. The transfer of the graphene film from the substrate S1 to
the substrate S2 can be accomplished by applying the substrate S2
onto the upper surface of the graphene film, followed by removal of
the substrate S1 (e.g. by dissolution of the substrate S1 or
peeling off the substrate S1).
[0111] Alternatively, the transfer can be accomplished by providing
a temporary material on the upper surface of the graphene film,
followed by removal of the substrate S1 (e.g. by dissolution of the
substrate S1 or peeling off the substrate S1) so as to obtain a
graphene film now having an uncovered lower surface and an upper
surface which is in contact with the temporary material,
subsequently applying the substrate S2 onto the lower surface of
the graphene film, followed by removal of the temporary material
(e.g. by dissolution of the temporary material or peeling off the
temporary material) from the upper surface of the graphene
film.
[0112] Applying the substrate S2 onto the lower surface of the
graphene film may include a thermal treatment, so as to improve the
adhesion between the substrate S2 and the graphene film.
[0113] With the term "temporary material", it is indicated that the
material is provided on the graphene film only temporarily and is
removed after the graphene film has been attached to the substrate
S2.
[0114] The temporary material can be a polymer. In the process of
the present invention, it is possible that the temporary material
such as a polymer is prepared on the upper surface of the graphene
film, e.g. by providing a precursor material (such as monomer
compounds or an uncured polymer resin) on the upper surface of the
graphene film, followed by converting the precursor material into
the temporary material (e.g. by polymerization of the monomer
compounds or a curing step). Alternatively, it is also possible
that the temporary material is prepared externally (i.e. not on the
graphene surface) and then provided on the uncovered upper surface
of the graphene film. For example a thermal release tape can be
applied to the upper surface of the graphene film under.
Preferably, such a thermal release tape is applied at mild
pressure. A thermal release tape as such is known, e.g. from Bae et
al., Nature Nanotechnology, 5, 574-578, 2010.
[0115] In a preferred embodiment, the temporary material is
provided on the upper surface of the graphene film by coating the
upper surface with a precursor material, followed by a treatment
step (such as polymerization, curing, etc.) so as to convert the
precursor material to the temporary material.
[0116] In a preferred embodiment which includes such a transfer, a
metal (such as copper) is used as substrate S1 and a curable
polymer such as polymethyl methacrylate PMMA (i.e. the precursor
material) is applied onto the uncovered upper surface of the
graphene film, followed by curing the curable polymer so as to
provide the temporary material. Subsequently, the metal substrate
S1 is removed, e.g. by dissolution in an appropriate etching
liquid, from the lower surface of the graphene film. Then, a
flexible and optionally transparent polymer foil (e.g. a
polyethylene terephthalate foil) is provided on the lower surface
of the graphene film, followed by removal of the temporary
material, e.g. by dissolution in an appropriate solvent.
[0117] After etching, the lower surface of the graphene film can be
targeted on the flexible substrate S2. Subsequently, spin-coating
can be used to remove the residual water between the graphene film
and substrate and increase the interfacial contact. Then, the
temporary material (such as PMMA) on the upper surface of the
graphene film can be removed and a thermal treatment at about
60-100.degree. C. can be carried out.
[0118] By using the process as described above, a layered assembly
comprising a graphene film on a substrate S1 or S2 may be
received.
[0119] The graphene films and layered assemblies may be used in
manufacturing electronic, optical, or optoelectronic device. Such
devices may be, without limitation, a capacitor, an energy storage
device, in particular a battery or supercapacitor, an inorganic or
organic field effect transistor device, an organic photovoltaic
(OPV) device, or an organic light-emitting diode (OLED). Further
suitable applications are electrochemical sensors, as well as fuel
cells.
[0120] The N content in the graphene can be determined by commonly
known analytical methods, such as .sup.1H-NMR spectroscopy,
.sup.13C-NMR spectroscopy, XPS (X-ray photoelectron spectroscopy),
IR spectroscopy and/or mass spectroscopy (e.g. matrix-assisted
laser desorption/ionization time of flight (MALDI-TOF) mass
spectroscopy).
[0121] According to a further aspect, the present invention
provides an electronic, optical, or optoelectronic device which
comprises a semiconductor film (e.g. a thin film) comprising one or
more of the graphene materials as described above.
[0122] Preferably, the device is an organic field effect transistor
device, an organic photovoltaic device, or an organic
light-emitting diode.
[0123] Customary and known equipment customarily used in the
semiconductor industry can be used for carrying out the process of
the invention.
[0124] All percent, ppm or comparable values refer to the weight
with respect to the total weight of the respective composition
except where otherwise indicated. The documents cited in the
present application are incorporated herein by reference in their
entirety.
[0125] The invention will now be described in further detail by the
following Examples without restricting the invention thereto.
EXAMPLES
Comparative Example C1
[0126] The graphene films were prepared in a hot wall CVD setup as
described in J. Am. Chem. Soc., 2011, 133, 2816-2819, modified with
a precursor inlet system allowing the supply of volatile
compounds.
[0127] Cu foils (7 cm.times.7 cm or smaller) were placed in a hot
wall furnace inside a quartz tube. The system was evacuated and the
leak rate was tested (leak rate: below 10.sup.-3 hPa/s). The system
was flushed with hydrogen gas by maintaining a pressure of 1.5 hPa
for cleaning the copper substrate. The tube was heated to
1000.degree. C. (hydrogen flow 150 cm.sup.3/min (NTP) at 1.5 hPa).
After reaching the desired temperature, 0.20 hPa partial pressure
of methane was allowed to react for 20 min at 1.5 hPa,
respectively, with or without additional hydrogen flow. After the
exposure, the furnace was allowed to cool to room temperature.
[0128] The resulting CVD samples on Cu foils were coated with poly
methyl methacrylate (PMMA) and then floated in dilute
Fe(NO.sub.3).sub.3 (0.05 g/ml). After dissolution of Cu, the
PMMA-coated film was transferred onto a quartz substrate. The PMMA
on the film was removed with acetone and the remaining graphene
film on quartz was washed with isopropyl alcohol.
[0129] The film morphology and the elemental composition of the
deposited graphene film were characterized by scanning electron
microscopy (SEM), transmission electron microscopy (TEM) and X-ray
photoelectron spectroscopy (XPS). The characteristics of the
resulting graphene layer are shown in Table 1 and 2.
Example 2
[0130] Comparative example C1 was repeated with 3.0 hPa partial
pressure of methylamine. The characteristics of the resulting
graphene layer are shown in table 1.
[0131] FIG. 2 shows Raman spectra indicating the formation of
unstructured carbon or high quality graphene in the case of methane
(example C1) and direct formation of graphene in the case of
methylamine with additional hydrogen present or absent in the gas
phase. This clearly reveals the precursor influence and the role of
hydrogen on the CVD of (doped) graphene films.
Example 3
[0132] Comparative example C1 was repeated with 3.0 hPa partial
pressure of ethylamine. The characteristics of the resulting
graphene layer are shown in table 1. The sheet resistance of the
deposited graphene was 3.2 10.sup.4 .OMEGA./sq.
Example 4
[0133] Comparative example C1 was repeated with 3.0 hPa partial
pressure of ethanol amine. The characteristics of the resulting
graphene layer are shown in table 1. The sheet resistance of the
deposited graphene was 1.9 10.sup.4 .OMEGA./sq.
Example 5
[0134] Comparative example C1 was repeated with 0.20 hPa partial
pressure of aniline. The characteristics of the resulting graphene
layer are shown in table 1.
Comparative Example C6
[0135] Comparative example C1 was repeated with 1.0 hPa partial
pressure of benzene. The characteristics of the resulting graphene
layer are shown in table 1.
TABLE-US-00001 TABLE 1 Peak positions and line widths (in cm-1) of
the Raman D, G and 2 D bands, intensity ratios of D and G peaks for
(N-doped) carbon and graphene films grown on copper with or without
the presence of hydrogen. D band G band 2D band Ex. Precursor Line
width Line width Line width I2D/IG C1 Methane --/1355 1584/1588
2714/-- 3.7/-- --/60 14/50 20/-- 2 Methyl 1370/1372 1588/1588
2720/2729 0.58/0.36 amine 33/46 25/29 40/55 3 Ethyl 1376/1376
1592.5/1592.sup. 2741/2741 0.90/0.48 amine 40/60 20/30 41/55 4
Ethanol 1367.5/1366.sup. 1585.5/1593.sup. 2729.5/2720.sup. 1.2/0.67
amine 32/34 19/23 52/38 5 Aniline 1370/1378 1587/1600 2731/--
0.78/--.sup. 70/150 18/70 32/-- C6 Benzene 1354/1378 1585/1602
2700/-- 3.6/-- 20/150 15/60 19/--
[0136] In general, the presence of the 2D band line width is in the
range of 40 cm.sup.-1 or smaller together with the narrow G band
and linewidth of 30 cm-1 or smaller indicates the formation of
graphene layers. Single layer graphene reveals a narrow G band with
line width lower than 30 cm.sup.-1 (usually in the range lower than
20 cm.sup.-1) and a high intensity of the 2D band (I 2D>I G)
which can be fitted by a single Lorentzian model. If other forms of
graphene (e.g. multilayer graphene) and carbon are present (e.g.
defective graphene), the intensity of the G and 2 D bands change
and the latter decreases. Although D modes are present in the
samples indicating defective and disordered carbon at 1350-1370
cm.sup.-1, the presence of graphene layers is unambiguously proven
by the presence of the narrow 2 D modes at approx. 2700 cm.sup.-1
and narrow line width. The Raman analysis of G mode around 1580
cm.sup.-1 and a line width better than 30 cm.sup.-1 in combination
with a 2D mode at 2700 cm.sup.-1 and a linewidth better than 40
cm.sup.-1 indicates the formation of graphene. N and O content of
the deposited graphene was determined by XPS analysis. Both N and
O-doping effects can also lead to the presence of D, and D modes in
addition to the G and 2D modes in the Raman spectra.
TABLE-US-00002 TABLE 2 XPS summary of the C/O/N-- ration of the
film surfaces: Example Precursor Conditions % C % O % N C1 Methane
no H.sub.2 59.54 39.86 n/a CH.sub.4 with H.sub.2 45.04 54.96 n/a 2
Methylamine no H.sub.2 71.60 28.40 <0.3 CH.sub.3--NH.sub.2 with
H.sub.2 78.10 21.90 <0.3 3 Ethylamine no H.sub.2 78.08 20.94
0.98 CH.sub.3--CH.sub.2--NH.sub.2 with H.sub.2 73.66 26.34 <0.3
4 Ethanolamine no H.sub.2 78.08 21.92 <0.3
HO--CH.sub.2--CH.sub.2--NH.sub.2 with H.sub.2 56.44 42.86 0.70 5
Aniline no H.sub.2 89.49 8.44 2.07 C.sub.6H.sub.5--NH.sub.2 with
H.sub.2 89.44 9.57 1.00 C6 Benzene no H.sub.2 86.63 13.16 n/a
C.sub.6H.sub.6 with H.sub.2 76.93 22.92 n/a
[0137] Due to the natural leak rate and samples exposed to air
after treatment oxygen was incorporated into the film.
[0138] The following analytical methods were used:
[0139] Chemicals were purchased from commercial suppliers: methane
(99.95%), pyridine (99.8%), acetonitrile (99.5%), ethylamine
(lecture bottle, 97%), methylamine (97%), nitro methane (98.5%),
nitrobenzene (99% extra pure), aniline (99%), benzene (99.5%) from
Sigma-Aldrich; nitro ethane (99%), Cu foils (25 .mu.m thickness,
99.8%) from Alfa Aesar; ethanol amine (99%) from ROTH. Liquid
precursors were dried and purified by standard distillation
techniques prior to use.
[0140] Determination of the film morphology and elemental
analysis:
[0141] Scanning electron microscopy (SEM) was performed with a
Zeiss LEO 1530 Gemini at 1.0 keV and Hitachi SU8000 at 1.0 keV. The
transmission electron microscopy (TEM) characterization was done
using FEI Tecnai F20. X-ray photoelectron spectroscopy (XPS) was
performed using a non-monochromatic Al K.alpha. photon source
(1486.6 eV) and a SPECS Phoibos 100 hemispherical energy analyzer.
Graphitic carbon materials deposited on a Cu foil were fixed on a
sample holder and introduced into the analysis chamber of a custom
made ultrahigh vacuum setup (base pressure at 10-10 mbar). The
atomic sensitivity factors of the core levels were provided by
SPECS. Raman spectra were measured with a BRUKER SENTERRA
Spectrometer (488 nm, 2 mW, 200 ms accumulation time, 50 .mu.m
aperture, the spectra were analyzed with a Lorentzian fitting). The
sheet resistance of transferred graphene films was measured by with
a JAN DEL micro positioning probe. The transparency of the graphene
films on glass substrates was measured with a PERKIN ELMER Lambda
900 UV/VIS/NIR spectrometer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0142] FIG. 1 shows a Raman spectrum of the graphene prepared from
methane according to comparative example C1.
[0143] FIG. 2 shows a Raman spectrum of the graphene prepared from
methylamine according to example 2.
[0144] FIG. 3 shows a Raman spectrum of the graphene prepared from
ethylamine according to example 3
[0145] FIG. 4 shows a Raman spectrum of the graphene prepared from
ethanolamine according to example 4
[0146] FIG. 5 shows a Raman spectrum of the graphene prepared from
aniline according to example 5
[0147] FIG. 6 shows a Raman spectrum of the graphene prepared from
aniline according to comparative example C6
[0148] The following embodiments are particularly preferred: [0149]
1. Use of an amine precursor of formula I
[0149] (X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I) [0150] or its
ammonium salt for depositing a graphene film having a nitrogen
content of from 0 to 65% by weight on a substrate S1 by chemical
vapor deposition (CVD), [0151] wherein [0152] R.sup.1 is selected
from [0153] (a) C.sub.1 to C.sub.10 alkanediyl, which may all
optionally be interrupted by at least one of O, NH and NR.sup.2,
[0154] (b) alkenediyl, which may all optionally be interrupted by
at least one of O, NH and NR.sup.2, [0155] (c) alkynediyl, which
may all optionally be interrupted by at least one of O, NH and
NR.sup.2, [0156] (d) C.sub.6 to C.sub.20 aromatic divalent moiety,
and [0157] (e) CO, CH.sub.2CO, [0158] X.sup.1 is selected from H,
OH, OR.sup.2, NH.sub.2, NHR.sup.2, or NR.sup.2.sub.2, wherein two
groups X.sup.1 may together form a bivalent group X.sup.2 being
selected from a chemical bond, O, NH, or NR.sup.2, [0159] R.sup.2
is selected from C.sub.1 to C.sub.10 alkyl and a C.sub.6 to
C.sub.20 aromatic moiety which may optionally be substituted by one
or more substituents X.sup.1, [0160] n is 1, 2, or 3. [0161] 2. The
use according to embodiment 1, wherein R.sup.1 is selected from
linear or branched C.sub.1 to C.sub.10 alkyl, which may optionally
be interrupted by O or NH, and a divalent C.sub.6 to C.sub.12
aromatic moiety. [0162] 3. The use according to embodiment 1 or 2,
wherein X.sup.1 is H and R.sup.1 is selected from linear or
branched C.sub.1 to C.sub.5 alkanediyl and a divalent C.sub.6 to
C.sub.12 aromatic moiety [0163] 4. The use according to embodiment
1 or 2, wherein X.sup.1 is selected from OH or OR.sup.2 with
R.sup.2 being selected from linear or branched C.sub.1 to C.sub.5
alkyl. [0164] 5. The use according to embodiment 1 or 2, wherein
X.sup.1 is selected from NH.sub.2, NHR.sup.2 or NR.sup.2.sub.2 with
R.sup.2 being selected from linear or branched C.sub.1 to C.sub.5
alkyl. [0165] 6. The use according to embodiment 1, wherein the
amine precursor is selected from methylamine, ethylamine, ethanol
amine, methyldiamine, ethylenediamine, aniline, and combinations
thereof. [0166] 7. The use according to embodiment 1, wherein the
amine precursor is selected from formamide and acetamide, or
combinations thereof [0167] 8. The use according to anyone of the
preceding embodiments, wherein the substrate S1 is selected from an
insulating, semiconducting or conducting substrate, or a
combination thereof, preferably a metal substrate. [0168] 9. A
process for depositing a graphene film having a nitrogen content of
from 0 to 65% by weight on a substrate S1, the process comprising
[0169] (a) providing an amine precursor of formula I
[0169] (X.sup.1--R.sup.1).sub.n--NH.sub.(3-n) (I) [0170] or its
ammonium salt for depositing a graphene film having a nitrogen
content of from 0 to 65% by weight on a substrate S1 by chemical
vapor deposition (CVD), [0171] wherein [0172] R.sup.1 is selected
from [0173] (a) C.sub.1 to C.sub.10 alkanediyl, which may all
optionally be interrupted by at least one of O, NH and NR.sup.2,
[0174] (b) alkenediyl, which may all optionally be interrupted by
at least one of O, NH and NR.sup.2, [0175] (c) alkynediyl, which
may all optionally be interrupted by at least one of O, NH and
NR.sup.2, [0176] (d) C.sub.6 to C.sub.20 aromatic divalent moiety,
and [0177] (e) CO, CH.sub.2CO, [0178] X.sup.1 is selected from H,
OH, OR.sup.2, NH.sub.2, NHR.sup.2, or NR.sup.2.sub.2, wherein two
groups X.sup.1 may together form a bivalent group X.sup.2 being
selected from a chemical bond, O, NH, or NR.sup.2, [0179] R.sup.2
is selected from C.sub.1 to C.sub.10 alkyl and a C.sub.6 to
C.sub.20 aromatic moiety which may optionally be substituted by one
or more substituents X.sup.1, [0180] n is 1, 2, or 3. [0181] (b)
providing the substrate S1, [0182] (c) if the amine precursor is in
the solid or liquid state, at least partly transferring the amine
precursor into the gas phase, [0183] (d) activating the amine
precursor in order to decompose the amine precursor, and [0184] (e)
depositing the graphene film on the substrate S1. [0185] 10. The
process according to embodiment 9, wherein in step c) amine
precursor is heated to a temperature of from 500.degree. C. to
1400.degree. C., preferably of from 600.degree. C. to 1300.degree.
C., most preferably of from 700.degree. C. to 1200.degree. C.
[0186] 11. The process according to embodiments 9 or 10, wherein in
step (d) and (e) the pressure is from 10.sup.-9 hPa to 500 000 hPa,
preferably from 10.sup.-9 hPa to 2000 hPa. [0187] 12. The process
according to anyone of embodiments 9 to 11, wherein the amine
precursor is selected from a C.sub.1 to C.sub.4 alkylamine and
steps (d) and (e) are performed in the presence of H.sub.2 in order
to deposit a graphene film being essentially free from nitrogen.
[0188] 13. The process according to anyone of embodiments 9 to 11,
wherein the amine precursor is selected from a C.sub.1 to C.sub.4
alkylamine and steps (d) and (e) are performed under inert
conditions in order to deposit a graphene film having a nitrogen
content of from 10.sup.-20 to 65% by weight. [0189] 14. The process
according to anyone of embodiments 9 to 11, wherein the amine
precursor is selected from a C.sub.1 to C.sub.4 alkanolamine and
steps (d) and (e) are performed in the presence of H.sub.2 in order
to deposit a graphene film having a nitrogen content of from
10.sup.-20 to 65% by weight. [0190] 15. The process according to
anyone of embodiments 9 to 11, wherein the amine precursor is
selected from a C.sub.1 to C.sub.4 alkanolamine or methylamine and
steps (d) and (e) are performed under inert conditions in order to
deposit a graphene film being essentially free from nitrogen.
[0191] 16. The process according to anyone of the preceding
embodiments, comprising a further step (f) transferring the
graphene film from the substrate S1 to a substrate S2, which is
different from the substrate S1. [0192] 17. A layered assembly
comprising a graphene film on a substrate S1 or S2, said layered
assembly being obtainable by the process according to one of the
embodiments 9 to 16, and said graphene film having a nitrogen
content of from 0 to 65% by weight. [0193] 18. An electronic,
optical, or optoelectronic device obtainable by a process according
to anyone of the embodiments 9 to 16. [0194] 19. The device
according to embodiment 18, wherein the device is a capacitor, an
energy storage device, in particular a battery or supercapacitor or
fuel cell, a field effect transistor device, an organic
photovoltaic device, or an organic light-emitting diode, a
photodetector or a electrochemical sensor.
* * * * *